Well-preserved low-Mg calcite tests of modern benthic foraminifera from a depth transect off SW Norway
show decreasing Sr/Ca with increasing water depth (r = –0.84). The Mg/Ca ratios also decrease with increasing water
depth, although in a curvilinear fashion. Moreover, the inter- and intra-species scatter is apparently larger than for Sr/Ca.
A majority of the analysed specimens have Mn/Ca < 200 μmol/mol, and show Sr/Ca, Mg/Ca that fall within published
ranges for benthic foraminiferal calcite, indicating that pristine biogenic calcite has been analysed. The uniform
temperature and salinity of bottom waters below ~800 m moreover indicate that neither temperature nor salinity can
explain the observed Me/Ca trends. The Sr/Ca and Mg/Ca depth trends cannot be explained by dissolution since bottom
waters are generally supersaturated with respect to calcite, and dissolution is only observed in a few specimens. Moreover,
a regular increase in sedimentary organic content with depth needed to invoke a decrease in porewater pH and
concomittant calcite dissolution is not observed. We tentatively ascribe the decreasing Sr/Ca and Mg/Ca trends to depthrelated
physiological phenomena. The relatively small intra- and interspecies scatter at a given water depth, as well as the
linear decrease in Sr/Ca ratios with increasing water depth observed in modern oceans, may render the Sr/Ca in calcitic
benthic foraminifera a potential water-depth proxy for fossil deposits.